Background Information

To be healthy, every part of the human body needs to be supplied with oxygen and nutrients. The blood's job is to travel
through the body's circulatory system (heart, lungs, veins, and arteries) picking up nutrients and oxygen and delivering
them to the other parts of the body. The heart acts as a powerful pump that generates the force necessary to move the
blood around the circulatory system. When something goes wrong with the body's circulatory system, it can lead to serious
health consequences or death.

The most common problem with the circulatory system is coronary heart disease, also called coronary artery disease.
Coronary heart disease is caused by the buildup of cholesterol and other material, called plaques, in the arteries.
This buildup is known as atherosclerosis. Over time as the plaques grow larger, the arteries, which usually carry
oxygenated blood to the heart, become narrower. As the arteries narrow they cannot carry as much blood to the heart.
The decrease in oxygenated blood can lead to chest pains and heart attacks. The plaques sometimes become dislodged and
form blood clots that block the blood flow—this can also cause heart attacks and strokes.

In this science activity students can model what happens to blood flow when coronary heart disease narrows a person's
arteries by comparing the flow of water (blood) through straws (arteries) of different diameters.

For Discussion

This science activity can be used as a starting point for a variety of science and health discussions. Here are a few
examples of questions that can be used to start a discussion:

Do you expect the cups to empty at the same or different rates? If you chose different rates, which one will empty
first? Why?

How can coronary heart disease be prevented?

What part of the circulatory system does the water represent in this activity? How about the other materials used?
Do they represent parts of the circulatory system?

Come up with examples of other places where diameter and flow rate matter. Think about examples in your home or in
manufacturing.

Materials

Needed for preparing ahead:

Scissors (1)

Food coloring (optional)

Water (enough to fill all the cups at least once)

Needed for each demo or small group at the time of the science activity:

Container for pouring water (1)

Plastic or Styrofoam cups (2); easier with 16 oz size or larger

Straws (2); make sure one has a larger diameter than the other

Play dough, clay, or silly putty

Pan or basin for catching water

Figure 1. A few simple household materials are all that are needed to do this fun science activity.

What to Do

Prepare Ahead (< 10 minutes)

Use the scissors to poke or cut a hole in the side of each cup, near the bottom. The holes should be approximately the same distance from the bottom of each cup. Widen the hole enough to comfortably fit each straw. The wider straw will need a bigger hole.

Trim the straws to approximately 2 inch lengths.

(Optional) Add food coloring to the water. This will make it easier for students to observe what is happening.

Science Activity (< 10 minutes)

Each group should have two cups: one with a large hole for the wider straw and one with a smaller hole for the slimmer straw. For each cup, put one straw in the hole. Make sure the hole is not squeezing the straw and narrowing it.

Use play dough, clay, or silly putty to seal the inside of the hole around the straw so that water cannot leak out of the hole.

Figure 2. Place play dough, or a similar material, around the straw on the inside of the cup to prevent leaking. Water should only be able to escape through the straw.

Place both cups in a pan or basin. Quickly fill both cups with water. Through which straw does the water
flow faster? Tips: The water is easier to see if it is colored. Either fill the cups at the same time, or
fill the cup with the smaller diameter straw first. Make sure the straws are pointing down so that the water can flow out.

Figure 3. Water will flow out of both straws, but at different rates.

Expected Results

You should see that the cup with the smaller diameter straw empties more slowly. This is because a pipe or straw
with a smaller diameter has a slower flow rate. This is also what happens in coronary heart disease. The arteries
(straws) become narrower (smaller diameter) due to the build-up of plaques. As the arteries narrow, they carry
blood (water) less quickly to the heart.

For Further Exploration

This science activity can be expanded or modified in a number of ways. Here are a few options:

Use play dough or other substances to model plaques inside the arteries (straws). What happens when the plaque
breaks away from the artery wall?

Make the activity quantitative by having students use stopwatches to time how long it takes to empty the cup
with different diameter straws. Graph the data.

Credits

You can find this page online at: http://www.sciencebuddies.org/science-fair-projects/Classroom_Activity_Teacher_Modeling_Blood_Flow.shtml

You may print and distribute up to 200 copies of this document annually, at no charge, for personal and classroom educational use. When printing this document, you may NOT modify it in any way. For any other use, please contact Science Buddies.